Current transformer



Oct. 15, 1929. E. PFHFFNER CURRENT TRANSFORMER Filed April 2, 1925 2 Sheets-Sheet 1929. E. PFIFFNER 1,731,865

CURRENT TRANSFORMER Filed April 1925 2 Sheets-Sheet 2 Patented Oct. 15, 1929 UNITED STATES MIL PFIFFNER, F FRYBOURG, SWITZERLAND CURRENT TRANSFORMER Application filed April 2, 1925, Serial No. 20,215, and in Germany February 2, 1924.

This'invention relates to improvements in current transformers particularly for high working voltages. In case the transformer is employed for lowvoltage a single transformer '5 is provided only, in which the high-tenslon winding and the low-tension winding maybe arranged on the same branch. However in case the transformer serves for transforming high-voltage currents, a number of single transformers are connected in series and the primary winding and secondary winding are arranged on two separated branches for the purpose of a better insulation. In the latter case for reducing the considerable stray it is necessary to arrange a compensating winding, which receives the field at the same energy in both branches of each single transformer.

Owing to the arrangement of the compensating winding the phase displacement is reduced to a minimum in high-voltage transformers provided with a number of seriesconnected single transformers and with separately arranged primary and secondary windings.

However the error between the primary current and secondary current still exists owing to the incomplete proportionality.

Transformers are already known in which 30 the deviation from the desired proportionality between the field and the current to be measured is obviated by the arrangement of a third winding of a condenser or by a separate auxiliary transformer between the current transformer and condenser.

The present invention has for its object to remove this drawback in that at first the magnetization current is correspondingly influenced and not the field.

According to the present invention this is accomplished by arranging a magnetically saturated iron path and an air-path disposed parallel thereto in the magnetic circuit of the transformer, whereby the proportionality between the component of magnetization and induction is obtained. The component of magnetization increased thereby is compensated by the charging current of a condenser.

According to requirement the condensers may be connected either to the secondary several modes of carrying out the present invention.

In the drawings Figs. 1 and 2 show one construction of the current transformer in longitudinal section, the section in Fig. 2 being taken at ninety degrees with respect to Fig. land part of the transformer being broken away in both figures.

Fig. 3 illustrates diagrammatically the arrangement of the windings of the magnetic circuit and the connection of the condenser of till e uppermost single transformer shown in Fig. 4 shows diagrammatically, as in Fig. 3, the arrangement of other single transformers.

Figs. 5, 6 and 7 illustrate other combinations of connecting single transformers.

Fig. 8 shows the vector diagram of the compensating arrangement, and

Fig. 9 the magnetization-line of the magnetic circuit of a single transformer.

Figs. 10 and 11 show modified constructions of connecting the compensating condensers in connection with induction coils.

The compensating current transformer for high voltages consists of a number of serieseonnected single transformers.

Each single transformer is enclosed in a casing 1 of insulating material, and the magnetic circuit of each transformer consists of branches 2, 2 and yokes 3, 3. The branch 2 is considerably reduced at 4, whereby an airgap 5 is formed, which does not extend through the entire width of the branch. The primary and secondary coils are mounted on insulating coil-supports 6 and 6', the top'coilsupport 6 carrying the primary winding and the compensating winding 8, while the bottom coil-support 6 carries the secondary winding 9 of the uppermost single transformer. Compensating windings 10 and 10 are arranged in close proximity of the branches within the coil-supports of both branches 2 and 2. A compensating condenser 11 is mounted above theyoke 3. The single transformers are mechanically. and electrically connected with one another by means of metallic rings 12 and 12', and the second electric connection is established by a centrally disposed support 13 of a conducting material.

The diagrammatic view of the single transformer shown in Fig. 3, illustrates the connection as used for the single transformer according to Figs. 1 and 2. 3, 3 and 2, 2' designate the magnetic circuit with the airgap 5 and the iron path or bridge 4. 7 represents the primary winding, 8 the compensatwinding, 9 the secondary winding and 10, 10 the compensating winding. In this construction the compensatingcondenser 11 is connected to the tension of the compensating winding 8.

In Fig. 3 an independent winding 8 is provided for feeding the condenser. The condenser is directly connected to the end of this winding. In this Fig. .3, the reference character 7 designates the primary windingand 9 represents the secondary winding. The winding 8 actsas secondary transformerwinding and compensates the magnetization current of the primarywinding 7 by means of the charging current of the condenser connected to it. A considerable leakage takes place if, in the case of transformers for high tension, the primary winding and secondary winding is arranged on two separate legs of the iron-core for, the purpose of a better in sulation. This leakage would produce a phase-displacement in both windings, which would considerably influence the exactness of measuring. The compensating windings 10 and 10' are arranged on both legs, in order to destroy the leakage. The two windings are connected directly with each other. The winding-direction of these two windings is such, that at a like number of windings in both windings the tensions produced by themain field are neutralized. The leakage fields produce compensating currents whose ampere-turns reduce the leakage field to aminimum.

- Figs: 4, 5, 6 and 7 illustrate some modified connections of the compensated current transformer. In the embodiment shown in Fig. 4, two iron paths 4, 4" and the corresponding air-gaps 5, 5 are provided in place of one iron path and one air gap only.

The compensating condenser 11 is connected to the compensating windings 10, 10'.

In, the modified embodiment shown in Fig. 5, the prlmary winding 7 and the secondary mamas winding 9 are disposed on the same branch,

In Fig. 7, the primary winding 7 and the secondary winding 9'are arranged on different branches and the condenser 11 is connected parallel with respect to the primary winding.

By means of the saturated iron path 4 and the air-gap 5, disposed parallel with respect to the iron path, it is rendered possible to place the ratio of the magnetizing ampere winding w, (Fig. 9) with respect to the induction B, as illustrated by the curve a in case of a pure iron path,-at the approximately straight line I) through the origin, e. g. to portionality.

The component of magnetization a, (Fig. 8), which becomes absolutely larger, now may be compensated. more or less exactly by an produce pro-' oppositely directed charging current component 2' In case the condenser is connected to a compensating Winding, a favourable influence by the" primary current or secondary current may be attained by suitably arranging the said winding. In order to obtain a certain shape of the curve of error, an induction coil 14 (Fig. 10) of a certain saturation of iron is connected parallel to the compensating condenser 11. If desired an additional condenser 15 (Fig. 11) may be arranged in the circuit of the induction coil 14.

Of course the present invention is not limited'to the constructions as above described and illustrated, as various modifications may be made without departing from the spirit of the invention.

1 claim-:-

1. A compensating current comprising a magnetic circuit, a magnetic resistance in said circuit, said resistance comprising a saturated iron path, an air gap disposed parallel to said iron path, a compensating winding for supplying a compensating circuit, a primary winding comprising two sections connected in series and disposed on each side of the said compensating winding and a secondary winding disposed in inductive relation to the mag-' netic circuit, the said compensating circuit being in inductive relation to the magnetic circuit.

2. A compensating current transformer comprising a magnetic circuit, a magnetic redisposed parallel to said iron path, a compensating Winding for supplying a compensating circuit, a primary winding for feeding" the compensating winding and a secondary winding disposed in inductive relation to the magnetic circuit, the said compensating circuit being in inductive relation to the mag netic circuit and inciuding acondenser.

3. A compensating current transformer comprising a magnetic circuit, a magnetic resistance in said circuit, said resistance com prising a saturated iron path, an air gap dis poscdparallei to said iron path, a compensatmg winding for supplying a compensating circuit, a primary winding for feeding the compensating winding and a secondary Winding disposed in inductive relation to the magnetic circuit, the said compensating circuit being in inductive relation to the magnetic circuit, and including a condenser and an induction coii,

4. A compensating current transformer comprising a magnetic circuit, a magnetic resistance in said circuit, said resistance cornprising a saturated iron path, an air gap dis posed paraiie to iron path, a compensating winding Ior suppiying a. compensating circuit, a primary Winding for feeding the compensating Winding and a secondary Wind ing disposed inductive relation to the mag" netic circuit, the said compensating circuit being in inductive reiation to the magnetic circuit, and comprising a piuraiity oi condensers'connected in paraiiei and in series ith an induction coil,

In testimony Wiriereoi E aftix my signature, 

